31 Oct 2012

Stunning new images released this week by the
European Southern Observatory (ESO) and the Hubble Space Telescope show
globular star clusters in spectacular detail.

Globular clusters are spherical groups of over hundreds
of thousands of ancient stars pulled toward each other by gravity. They are
amongst the oldest objects in the universe, and for many years astronomers have
used them to study the structure and evolution of stars.

Globular clusters are very common; our galaxy alone
has about 150 million visible clusters orbiting its periphery, and many remained undiscovered.

This wide view of the globular star cluster NGC 6362 was
captured by the 67-million pixels Wide Field Imager (WFI) attached to the MPG/ESO 2.2-metre telescope at La Silla Observatory in Chile. This is one of many new color images created from data obtained during the ESO Imaging Survey concluded in 2002.

Wide view of NGC 6362 captured by the Wide Field Imager in MPG/ESO 2.2-metre telescope (credit: European Southern Observatory)

This survey collected
images of several regions of the sky in preparation for observations with the new
huge Very Large Telescope (VLT). ‘The full set of data obtained by the
ESO Imaging Survey would be better compared to a set of maps’ says Richard
Hook, ESO’s public information officer.

Another dazzling image
of NGC 6362 was created combining ultraviolet, visible-light and infrared images
taken by the Hubble Space Telescope- a space-based observatory run by the
European Space Agency and NASA.

This view takes a
closer look at the compact core of the globular cluster. Hook says ‘[Research] groups
are combining WFI and Hubble data on globular clusters very successfully in
other projects.’ The wide-angle and detailed views from these two telescopes ‘complement
each other perfectly’.

Most stars in a
globular cluster are over 10 billion years old, nearly as old as the universe
itself, and they look typically yellowish or red. In recent years, however, younger-looking
massive blue stars- blue stragglers- have been found in the core regions of star
clusters, including NGC 6362.

Since all stars in a
globular cluster were presumably born at the same time and therefore have
similar ages, astronomers came up with two theories to explain blue stragglers:
they must be the result of a star collision or a transfer of material between
two neighboring stars.

The Paranal platform of the Very Large Telescope (VLT) with the four main units and four auxiliary telescopes (credit: ESO/H.H.Heyer)

The new images from ESO’s WFI/2.2-meter and Hubble
telescopes will help astronomers from over 25 countries solve this and many other mysteries.

It will be exciting to see new answers and questions arise with the new generation of powerful super-telescopes like the VLT.

30 Oct 2012

The 'travelling salesman problem' has puzzled mathematicians for
over eight decades, but bees might just have the answer. In a study published in September in the journal PLoS Biology, scientists show that bumblebees quickly
work out the shortest route to feed from several flowers and return to their
nest.

Pollinator insects like bumblebees, and other foraging animals
such as hummingbirds, bats and even primates, establish stable routes between
regular feeding sites and their homes. To save energy, foragers have to come up
with a way of visiting multiple locations while traveling the shortest possible
distance. This is a task identical to the travelling salesman mathematical
problem, which tries to calculate the shortest route to visit several cities
once and return to the starting point. Now Lars Chittka's team at Queen Mary
University of London found how bees manage to solve this problem without
computers or even a map. Andy Reynolds from Rothamsted Research and a co-author in the
study says 'We showed how this complex routing problem can be solved by
small-brained animals without requiring 'map-like' memory'.

The scientists trained bees to collect sugar from artificial
flowers, and then followed their flying routes from the nest to five artificial
flowers arranged as a pentagon in a field. To do this, they attached a tiny
wire antenna to the back of each bee and tracked their movements with a radar,
much like a GPS navigation system. They found that the bees first visited the
nearest flowers to the nest, and that, in only eight round-trips, they had
discovered all the flowers. After this initial 'random' explorative phase, the
bees gradually began visiting the flowers in a specific sequence, as though in
each trip they were learning and progressively optimizing the 5-flower circuit.

Amazingly, in just about a couple dozen trips, each bee chose
the shortest possible route to visit all five flowers and return to the nest-
amongst the 120 other possible ways- and stuck to it 'Stable routes (...) that linked together all the flowers in an
optimal sequence were typically established after a bee made 26 foraging bouts,
during which time only about 20 of the 120 possible routes were tried.'
explains Reynolds.

But what happens if the flower spatial arrangement changes? In
the wild, bees have to modify their foraging routes in response to changes in
the environment. To understand how bees do this, the scientists removed an
artificial flower from the pentagonal experimental set-up and tracked the bees with
the radar. They found that the bees continued to visit all four flowers and the
empty feeding location using the optimal route, as if they could remember where
the missing flower had been.

Previous work on honeybees suggested that bees have a 'map-like
memory', but the authors in this study believe bees can develop optimal routes
simply by using 'a highly effective and versatile trial and error method'
Reynolds says. The scientists used their experimental data to develop a
mathematical 'trial and error' model based on heuristic, or experience-based,
algorithms. Similar heuristic models describing how ants find the shortest
routes between feeding locations and their nest are widely used by
mathematicians and computer scientists. These models work only for a low number
of locations, however, and in nature bees can feed from hundreds or even
thousands of flowers. So what happens then? Reynolds explains 'The trial-and-error model becomes impractical for 20 or more
locations but is effective for up to about 10 locations, which in practice
could facilitate the linking up of flower patches'.

Bees may move randomly between flowers within a flower patch,
but have a fixed order of flying between patches. 'This could be quite
effective because there could be much to gain by minimizing the distances flown
between patches but little to gain by minimizing the distances flown within
patches' he says.

The team had recently made similar observations in the
laboratory, but this is the first study examining the bee's routing behavior
over long distances and in a natural setting. Thomas Collett, a neurobiologist
at the University of Sussex who specializes in insect navigation says 'Such a study of the ontogeny of routes over the kinds of
distances that bumblebees normally fly has had to wait for the right
technology'.

In the future, Chittka's team would like to use their radar
tracking method to answer questions such as whether bees can solve the
travelling salesmen problem when more feeding sites are available. Collett says
'Testing [this] and other models will be exciting and may give new insights
into navigation and sequence learning'.

This article was published in The Munich Eye on the 27th of September 2012. You can read it here.Source:Lihoreau et al PLoS Biology (2012) DOI: 10.1371/journal.pbio.1001392

27 Oct 2012

For
sea urchin sperm, finding an egg to fertilize in a vast ocean might seem like
looking for a needle in a haystack. However, these prickly creatures have
devised a highly effective strategy to overcome this hurdle: eggs release
chemical factors that guide the sperm towards them, a process called
chemotaxis. Now, scientists from the Center of
Advanced European Studies and Research in Germany have discovered how sea
urchin sperm navigate up a gradient of attractant.

Tracking of calcium signals (green) from a sperm cell swimming in a chemoattractant gradient (blue)(credits: Luis Alvarez and René Pascal from Stiftung Caesar)

Sperm
chemotaxis is commonly found in nature and is important for fertilization. Most
animal species with external fertilization- such as marine invertebrates like
sea urchins- and even some plants, use chemical
attractants to guide sperm towards the egg. However, the molecular details of sperm
chemotaxis, particularly in mammals, such as humans, are still not well
understood.

Research on mammalian sperm chemotaxis presents many challenges: direct measurements can only be carried out in vitro and only about 10% of sperm respond to
attractants. In contrast, fertilization in sea urchins can be mimicked
in the laboratory, and 'sperm are mostly homogeneous in their responses' the researchers say.

When
sea urchin sperm detect an attractant, they adjust their swimming trajectory by
changing the beating of the tail (flagellum). The attractant
of Arbacia punctulata, the sea urchin
species used in this study,is a
small molecule called 'resact'. Resact released by the egg binds to receptor
proteins on a sperm’s flagellum, and this causes calcium ions to enter the cell.
The calcium rise controls the flagellar beat and tunes the swimming path of sperm, but exactly how this happens remains unclear.

In
the study published in September in The Journal of Cell Biology, Benjamin Kaupp’s
group shows how sea urchin sperm sample and integrate the attractant cues to adjust
their course as they swim towards the egg.

Sperm oozing out
of the sea urchin gonopores (credit:René
Pascal from Stiftung Caesar)

The
scientists placed sea urchin sperm in tiny chambers and then added caged resact, a modified version of the molecule that is activated by a flash of UV
light. Using caged resact, the scientists were able
to stimulate the sperm with the attractant at precise time intervals. They
found that sperm count resact molecules for about 0.2 to 0.6 seconds before
producing a calcium response- they called this 'sampling time'. 'A defined or
optimal sampling time is essential,' says Nichiket Kashikar, leading author in the study 'either too
short or too long sampling times will leave the sperm astray'.

Sperm
are also able to correct themselves, for instance, by stopping a calcium
response and initiating a new one, or 'resetting'. But
how does resetting affect swimming? To answer this question, the scientists recorded
videos of single sperm cells stimulated with resact during a calcium surge. 'During the
reset, sperm show an extended period of straight swimming, thereby spending more time swimming up the gradient of
attractant.' explains Kashikar 'Simple
rule: if the conditions are improving, continue in the same direction'.

The
authors propose that this newly found sperm 'navigation system' might be used
by other species. 'Although there are likely to be species-specific
differences, there might be some commonalities across species' Kashikar says. It remains to be discovered whether
similar mechanisms exist in human sperm.

'Chemotaxis is clearly important
for sea urchins' notes David Clapham, an expert on calcium sensors from the Howard Hughes Medical
Institute Boston Children’s Hospital in the United States 'However,
[in mammals] investigators will have to demonstrate that a
progesterone gradient exists in the path of swimming sperm in females and that
sperm respond to this gradient, not the factor alone'.
Kaupp’s team trusts that this might be possible in a near future. 'The
experimental tools developed to study chemotaxis in model systems (such as sea
urchin) and the chemotactic principles identified might help to design
experiments to study chemotaxis of sperm in human and other mammalian species'.

A shorter version of this article was published in ScienceNow on the 19th of September 2012. You can read it here.

26 Oct 2012

Scientists have discovered that
cancers are fueled by small populations of cancer stem cells. These cells are
resistant to current therapies and are thought to drive cancer relapse and
metastasis, which are the main cause of death in cancer patients. The exciting
findings published in August in the journals Nature and Science could lead to
revolutionary new strategies for cancer treatment.

Cancer is the second cause of death
in the US and Europe, and despite an increase in cancer survival in some
cancers due to prevention and early diagnosis, the survival rate for patients
with cancers in advanced stages has not changed significantly in the past
decades.

After a tumor is removed surgically
or by chemo and radiotherapy, it often grows back (relapse) and spreads to
other parts of the body (metastasis). Scientists have believed for many years
that a small population of cancerous stem cells is resistant to therapy and
responsible for tumor growth, including during relapse and metastasis- this is
called 'cancer stem cell hypothesis'.

During the past 15 years, several
research groups have described cancer stem cells in many types of cancer, and
transplantation experiments, in which cells from biopsies of cancer patients
are injected into mice, have shown that such cells could generate new tumors.
However, these studies did not provide direct evidence for the existence of
cancer stem cells. "This manipulation of tumors could potentially bring
pitfalls and stronger evidence from unperturbed tumors were needed," said Gregory Driessens, a molecular biologist from the Université Libre de Bruxelles in Belgium.

Now researchers from three
independent groups were able to 'see' cancer stem cells labeled with
fluorescent markers promoting tumor growth in the brain, skin and digestive
system of mice. "Our finding confirms that cancer stem cells really exist
as it was suggested but not formally proven so far by grafting
experiments," said Driessens, who led the study that identified
cancer stem cells in skin.

Cancer stem cells consist of only
about 1-3% of all cells in a tumor. So why is their discovery so important?
Cancer stem cells could be the source of the most aggressive cancers with a
poor prognostic. "This the first time researchers have traced the cell of
origin within different tumors. Because cancers are proving to be so complex,
we don't yet know how relevant this research in mice is to humans, but it gives
us new insights into how cancers might develop and why they can sometimes grow
back after therapy." explains Michaela Frye, a Cancer Research UK
scientist based at the University of Cambridge (UK).

"Anticancer treatments should
not only be evaluated on their efficacy on the bulk tumor but also specifically
for the effect on cancer stem cells, since these cells could be more resistant
to chemo and radiotherapies," adds Driessens. These discoveries
therefore open the way for the development of new therapies targeting cancer
stem cells, which could revolutionize the treatment of cancer.

This article was published in The Munich Eye on the 14th of September 2012. You can find it here.